V2-like vasopressin receptor mobilizes intracellular Ca2+ in rat medullary collecting tubules

Abstract

Cytosolic free calcium concentration ([Ca2+]i) was measured in single microdissected rat medullary collecting tubules [outer (OMCD) and inner (IMCD)] to identify receptors involved in vasopressin (AVP)-induced [Ca2+]i increases. In both segments, [Phe2,Orn8]vasotocin ([Phe2,Orn8]VT), a specific V1 agonist, as well as the V2 agonist 1-desamino-8-D-AVP (dDAVP) triggered [Ca2+]i variations. In OMCD, the mean response to 10 nM AVP roughly corresponded to the sum of V1 and V2 agonists effects. In IMCD, dDAVP (10 nM) alone reproduced the calcium response to AVP (delta[Ca2+]i = 243 +/- 34 nM, n = 6, and 248 +/- 27 nM, n = 8, with dDAVP and AVP, respectively). Furthermore, in the same experiments V1 and V2 maximal effects were not additive ([Phe2,Orn8]VT = 154 +/- 21 nM, n = 6; dDAVP + [Phe2,Orn8]VT = 233 +/- 23 nM, n = 9). As AVP, dDAVP released intracellular calcium (delta[Ca2+]i in calcium-free medium = 182 +/- 24 nM, n = 8, vs. 182 +/- 14 nM, n = 6 with 10 nM dDAVP and AVP, respectively). Neither 8-(4-chlorophenyl-thio)-adenosine 3',5'-cyclic monophosphate nor forskolin modified [Ca2+]i. A cross-reaction of dDAVP with an oxytocin (OT) receptor can be excluded since 1) the specific OT agonist [Thr4,Gly7]OT (10 nM) increased only slightly [Ca2+]i (delta-[Ca2+]i = 20 +/- 5 nM, n = 11); 2) the dDAVP response was not altered by the specific OT antagonist [1-(beta-mercapto-beta,beta-cyclopentamethylene propionic acid),2-(O-methyl)tyrosine,4-threonine, 8-ornithine,9-tyrosylamide]vasotocin [d(CH2)5(1),O-Me-Tyr2,Thr4,Tyr-NH2(9)]OVT; 3) it was insensitive to V1 antagonists but was totally blocked by the V1/V2 antagonist [d(CH2)5(1),O-Et-Tyr2,Val4]AVP ([delta[Ca2+]i = 18 +/- 4 nM, n = 6). These results indicate that in IMCD AVP increases [Ca2+]i via both V1 and V2 receptors. [Ca2+]i variations due to V2 receptors involve a mechanism independent of adenylate cyclase and coupled to the same intracellular calcium pool as V1 and V2 receptors.

Vasopressin-stimulated Ca 2+ reabsorption in rabbit cortical collecting system: effects on cAMP and cytosolic Ca 2+

“…7). A similar dual coupling mechanism has been postulated for the V2 receptor in the rat medullary collecting duct [11,14,24]. Further more, Zhu et al [36] have demonstrated that, when overexpressed in vitro, the human V 2 receptor has the capacity to couple to both adenyl cyclase and phosphoinositide-specific PLC.…”

“…This effect was independent of cAMP, since it was not mimicked by forskolin. Interestingly, cAMP-independent effects of dDAVP on [Ca2*]j have also been report ed for microdissected rat outer and inner medullary col lecting tubules [11,14,241. Similarly, AVP evoked a transient increase in [Ca2*^ in the complete absence of external Ca2+.…”

The physiological and pathophysiological functions of renal and extrarenal vasopressin V2 receptors

“…Coupling of V2Rs to adenylyl cyclase takes place after AVP binding and increases catalysis of ATP into cAMP, activating protein kinase substrates (e.g., PKA). An increasing understanding of the modalities involved in V2R signaling indicates that V2R also increases intracellular Ca 2ϩ (20,33,106,133). Furthermore, V2R-mediated AQP2 trafficking is now known to be calmodulin dependent (23).…”

PTH-independent regulation of blood calcium concentration by the calcium-sensing receptor

“…Double wavelength measurements of Fura-2 fluorescence were carried out after a 30-minute equilibration period with a standard photometric set up (model MSP 21) assisted by a microcomputer (51). As a rule, all tubules were studied within less than 1 hour following their microdissection.…”